U.S. patent number 4,131,664 [Application Number 05/837,313] was granted by the patent office on 1978-12-26 for method of making a multiple-density fibrous acoustical panel.
This patent grant is currently assigned to Allen Industries, Inc.. Invention is credited to Thomas A. Flowers, Anthony W. Marra, Samuel D. Vinch.
United States Patent |
4,131,664 |
Flowers , et al. |
December 26, 1978 |
Method of making a multiple-density fibrous acoustical panel
Abstract
An improved acoustical and trim acoustical panel suitable for
use in the interior passenger compartments and exterior components
of automotive vehicles or the like, comprising a plurality of
fibrous layers of controlled different density, integrally united
together at their interfaces and optionally provided with a
decorative finish on one or both outer face surfaces thereof. The
invention is further directed to novel methods for making such trim
panels incorporating preselected contours and localized embossments
therein to conform to the contour of the structural panels of
vehicle bodies over which the trim panels are adapted to be
mounted. In accordance with one process embodiment, a fibrous pad
is formed incorporating suitable binding agents and a coextensive
impervious membrane or film disposed intermediate of the face
surfaces thereof. The composite pad is placed in an appropriately
contoured mold and pneumatic pressure is applied to one side
thereof to effect a densification and molding of the stratum of
fibers disposed between the membrane and the mold surface without
appreciably compacting the opposite fibrous layer, while
simultaneously setting the binding agent to form a contoured
shape-retaining pad having a dual-density fibrous structure.
Inventors: |
Flowers; Thomas A. (Royal Oak,
MI), Marra; Anthony W. (Sterling Heights, MI), Vinch;
Samuel D. (Detroit, MI) |
Assignee: |
Allen Industries, Inc. (Troy,
MI)
|
Family
ID: |
25274140 |
Appl.
No.: |
05/837,313 |
Filed: |
September 28, 1977 |
Current U.S.
Class: |
264/510; 156/285;
264/118; 428/218; 264/113; 264/119 |
Current CPC
Class: |
B29C
43/203 (20130101); B29C 70/28 (20130101); B32B
27/12 (20130101); B32B 1/00 (20130101); B32B
27/32 (20130101); B29K 2105/0854 (20130101); Y10T
428/24992 (20150115); B32B 2307/102 (20130101); B32B
2309/105 (20130101); B32B 2307/718 (20130101); B32B
2607/00 (20130101); B32B 2307/304 (20130101) |
Current International
Class: |
B32B
27/12 (20060101); B29C 017/04 (); B32B
001/10 () |
Field of
Search: |
;264/89,90,91,92,93,113,118,119 ;156/285 ;428/218 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Silbaugh; Jan H.
Attorney, Agent or Firm: Harness, Dickey & Pierce
Claims
What is claimed is:
1. The method of making an acoustical and thermal insulating
fibrous panel which comprises the steps of forming a composite
fibrous pad comprising a first fibrous layer and a second fibrous
layer disposed in overlying relationship each of substantially
uniform thickness and density incorporating a binding agent
distributed therethrough and a flexible impervious film disposed
between the opposed faces of said first layer and said second
layer, positioning said pad with said first layer disposed in
overlying relationship adjacent to a mold having a preselected
contour, applying a pneumatic pressure through said second layer
against said film of a magnitude sufficient to effect a compaction
of said first layer between said film and said mold to a desired
density and in shape-conforming contact with said mold without
effecting any appreciable densification of said second layer,
setting said binding agent to retain the fibrous layers in the
preselected contoured configuration and said first layer in the
densified condition, and thereafter releasing said pneumatic
pressure and extracting the contoured dual-density trim panel from
said mold.
2. The method as defined in claim 1, in which said film is
coextensive with said first and second layer and is of a thickness
ranging from about 0.0005 to about 0.025 inch.
3. The method as defined in claim 2, in which said first and second
layer of said composite fibrous pad are of a weight of about 50 to
about 500 grams per square foot.
4. The method as defined in claim 1, in which said film is of a
thickness of about 0.001 to about 0.005 inch.
5. The method as defined in claim 1, in which said first and second
layer of said composite fibrous pad are of a weight of about 100 to
about 200 grams per square foot.
6. The method as defined in claim 1, in which said composite
fibrous pad is formed to a thickness of about 0.5 to about 5
inches.
7. The method as defined in claim 1, in which said composite
fibrous pad is formed to a thickness of about 1.5 to about 3
inches.
8. The method as defined in claim 1, in which said binding agent is
present in an amount of about 10% to about 45% by weight of the
total weight of each of the layers.
9. The method as defined in claim 1, in which said binding agent is
heat-activatable and including the further step of heating said
composite pad while in said mold under pneumatic pressure to effect
a heat setting of said binding agent.
10. The method as defined in claim 1, in which the step of applying
pneumatic pressure against said film is performed to control the
pressure on said film within a range of about 20 to about 50
psig.
11. The method as defined in claim 1, including the further step of
subjecting said composite fibrous pad to a preliminary cure
treatment to partially set said binding agent in the stratum
adjacent to the outer faces of the fibrous layers.
12. The method as defined in claim 1, including the further step of
applying a porous sheet to at least one exposed face of said
composite fibrous pad prior to the molding step.
13. The method as defined in claim 1, in which the step of forming
said composite fibrous pad includes the further steps of separately
forming said second layer, applying said film over one face of said
second layer, and thereafter applying said first fibrous layer over
said film.
14. The method as defined in claim 13, in which said first layer is
separately formed to the desired thickness and density and
thereafter is applied over said film.
15. The method as defined in claim 13, in which said first layer is
formed in situ on said film.
16. The method as defined in claim 1, in which the step of forming
said composite fibrous pad includes the further steps of forming an
integral fibrous web of the desired thickness and density, slitting
said web intermediate of the face surfaces thereof into said first
layer and said second layer, and interposing said film between the
opposed slit faces of said first and second layer.
17. The method as defined in claim 1, including the further step of
providing said mold with a preselected textured surface over at
least a portion of the surface area thereof to impart a
corresponding texture to the exposed face of said first layer.
18. The method as defined in claim 1, including the further step of
substantially sealing the peripheral edge of said composite fibrous
pad prior to the application of pneumatic pressure thereto.
Description
BACKGROUND OF THE INVENTION
A variety of materials and structural arrangements, as well as
processing techniques for their manufacture, have heretofore been
used or proposed for use for producing acoustical and trim
acoustical panels of a type adapted to be installed against the
interior surfaces of structural panels, defining the passenger
compartment of automotive vehicles or the like. Such panels have
been effective in reducing the transmission of engine and road
noise into the passenger compartment and in some instances, have
also been employed to further enhance the aesthetic decor of the
passenger compartment by the application of suitable finishes to
the exposed face of the panel. The important considerations
heretofore associated in the manufacture and use of such panels has
been the cost of the material itself, the cost of its manufacture
and the ease by which such panels can be installed at selected
locations adjacent to the structural panels defining the vehicle
body. A further important consideration has been the acoustical
property of such panels and their durability over prolonged service
during which they are subjected to wide variations in ambient
conditions.
Composite, contoured sound insulating panels which have been
commercially acceptable typically comprise a fibrous pad having a
dense filled resinous or asphaltic coating applied substantially
uniformly on at least one face surface thereof. Prior art processes
typically employed for manufacturing such composite sound
insulating panels are disclosed in U.S. Pat. Nos. 3,429,728;
3,536,557 and 4,035,215. In accordance with the foregoing patented
processes, fibrous panels are molded to impart a preselected
shape-sustaining contour thereto and are coated with a dense sound
insulating substance, such as a highly filled asphaltic or
bituminous base material, or alternatively, a highly filled
thermoplastic resinous material such as a plastisol, for example.
The composite structure of such panels has contributed to a
significant reduction in the noise level of passenger compartments
of automotive vehicles.
The energy crisis has prompted an increased emphasis on the
manufacture of more fuel efficient automobiles and reductions in
the size and weight are important considerations in attaining this
goal. In the selection of lighter weight materials and structural
components to achieve a reduction in the weight of the vehicle,
careful consideration has been given to the maintenance of
passenger safety and comfort. There, accordingly, has developed a
need for an improved acoustical and trim acoustical panel which is
of lighter weight, but which nevertheless provides for satisfactory
sound and thermal insulating characteristics, which is of
economical manufacture, which is simple to install and which
provides for versatility in its use at selected locations in
automobile bodies or the like.
The present invention provides for an improved acoustical trim
panel as well as for novel methods of producing such trim panels on
a commercial scale at economical cost, whereby sound insulating
characteristics are retained at a substantial reduction in weight
of such panels.
SUMMARY OF THE INVENTION
The benefits and advantages of the present invention are achieved
by a fibrous panel possessed of acoustical properties and
comprising a plurality of fibrous layers, each of a controlled
different density disposed in substantially coextensive overlying
relationship and integrally united to each other at the interface
therebetween. Each of the fibrous layers is comprised of a fibrous
mass of substantially uniform density and thickness over the major
area thereof and a suitable binding agent of a thermosetting or a
thermoplastic type, as well as mixtures thereof, present in amounts
ranging from as low as about 10% up to about 45% by weight based on
the total weight of the fibrous layer. The panel may further
incorporate local embossments characterized by areas in which all
of the fibrous layers are densified so as to provide for further
rigidification of the panel as well as to conform to the surface
contour of the structural panels over which the panel is adapted to
be installed. The panel may further include one or more films
interposed between the exposed face surfaces of the panel
positioned at selected areas as well as extending coextensively of
the periphery of the panel itself to further enhance the acoustical
characteristics thereof.
In accordance with the method aspects of the present invention, the
plural density acoustical panel is made in accordance with one of
the process embodiments by first forming a composite fibrous pad
containing a flexible film or membrane interposed between a first
fibrous layer and a second fibrous layer disposed in overlying
relationship. Each of the fibrous layers are initially of
substantially uniform thickness and density and incorporate a
suitable binding agent distributed therethrough. The composite
fibrous pad is thereafter subjected to a molding operation whereby
the pad is positioned in overlying relationship with respect to a
mold having a preselected contoured mold surface and a pneumatic
pressure is applied through the opposite fibrous layer against the
flexible film or membrane at a pressure sufficient to effect a
compaction of the fibrous layer disposed between the film and the
mold surface to a desired density and in intimate contact with the
mold surface without effecting any appreciable densification of the
opposite fibrous layer. While under the pressurized condition, the
binding agents in the fibrous pad are set or cured so as to retain
the densified fibrous layer, as well as the nondensified fibrous
layer in the appropriately contoured and densified condition.
Thereafter, the pressure is released and the panel is extracted
from the mold.
In accordance with an alternative process of the present invention,
each of the individual fibrous layers are separately molded between
contoured mold surfaces to the desired density and configuration.
The opposed surfaces of the individual layers are thereafter coated
with a suitable adhesive and the layers are assembled in
superimposed overlying relationship and are subjected to a final
molding operation between matched pairs of mold surfaces, forming
an integral acoustical panel comprised of a plurality of fibrous
layers of controlled different densities.
In accordance with still another alternative method of the present
invention, a contoured multi-layered panel is produced by first
molding a lower density fibrous pad to a desired preselected
contoured configuration and forming a second fibrous pad
incorporating a thermoplastic binder therein in the form of a flat,
high density layer. The high density pad is preheated to a
temperature to effect a heat softening of the thermoplastic binder
therein, whereafter the heat softened high density layer is
superimposed over the precontoured low density layer, with a
suitable bonding agent interposed therebetween, and the assembly is
subjected to a final molding operation in which the heat softened
high density layer is cooled to a temperature below that at which a
rigidification of the thermoplastic binding agent occurs and a
setting of the adhesive is effected, producing a shape-retaining
dual-density composite fibrous acoustical panel.
Additional benefits and advantages of the present invention will
become apparent upon a reading of the description of the preferred
embodiments, taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a typical fibrous panel assembly of
a type to which the present invention is applicable;
FIG. 2 is a fragmentary transverse sectional view through the panel
shown in FIG. 1 and taken substantially along the line 2--2
thereof;
FIG. 3 is a fragmentary and partially schematic side elevational
view of a typical press arrangement for molding the fibrous panels
of the present invention;
FIG. 4 is a fragmentary perspective view, partly in section,
illustrating the disposition of a composite fibrous pad positioned
on one mold surface preliminary to closing of the upper mold;
FIG. 5 is a fragmentary magnified elevational view of the composite
fibrous pad interposed between the closed mold surfaces of FIG. 3
prior to application of fluid pressure to an impervious film
interposed between the face surfaces of the pad;
FIG. 6 is a fragmentary magnified sectional view similar to FIG. 5
illustrating the disposition of the fibrous pad after the
application of a controlled pneumatic pressure against the
underside of the impervious film;
FIG. 7 is a fragmentary perspective view of one technique for
forming a composite fibrous pad for molding in accordance with the
procedure depicted in FIGS. 3-6;
FIG. 8 is an alternative technique for producing a composite
fibrous pad incorporating an impervious film interposed between the
face surfaces thereof;
FIG. 9 is still another alternative method for forming a composite
fibrous pad incorporating an impervious film therethrough;
FIG. 10 is a fragmentary perspective view of two independently
contoured fibrous layers of controlled different densities which
are adhesively secured to form a dual-density fibrous panel;
FIG. 11 is a fragmentary side elevational view, partly in section
and partly schematic, illustrating a press arrangement for final
molding the assembly of FIG. 10;
FIG. 12 is a fragmentary perspective view of a low density
separately controued fiber layer and a higher density heat softened
fibrous layer adapted to be applied in superimposed relationship
over the low contoured layer;
FIG. 13 is a fragmentary side elevational view, partly in section
and partly schematic, illustrating a press arrangement for final
cold molding the fibrous assembly of FIG. 12.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now in detail to the drawings, a typical multiple-layered
fibrous acoustical panel of the type to which the present invention
is applicable is illustrated in FIG. 1. As shown, the panel 20 is
possessed of a compound curvature of any desired configuration
conventionally corresponding to the curvature of the structural
floor panel of an automobile body over which the acoustical panel
is adapted to be installed. As may be best seen in the magnified
cross sectional view comprising FIG. 2, the panel 20 includes a
first or densified fibrous layer 22 and a second fibrous layer of
lower density indicated at 24, which are integrally united together
at the interface therebetween. In the specific embodiment shown,
the acoustical panel includes a compacted densified peripheral edge
portion 26 extending therearound to facilitate attachment of the
panel and can further include a densified strip or rib over
localized areas thereof for the purpose of imparting further
rigidity to the panel, as well as for providing clearance or
accommodating structural stringers on the surface of the panel over
which the acoustical panel is to be secured. Additionally, the trim
panel 20 can be provided with one or more cut-out sections or
apertures 30, as may be desired or required, through which
structural components of the vehicle body project. The aperture 30
conventionally is cut through the panel upon completion of the
molding thereof. In addition to apertures 30, the panel can be
provided with suitable slits, perforations, etc., at selected
locations to accommodate control and operating linkages.
While the specific embodiment illustrated in FIGS. 1 and 2
illustrate an acoustical panel comprised of two fibrous layers of
different density, it will be appreciated that the present
invention is also applicable for the fabrication of acoustical and
trim acoustical panels comprising three or more fibrous layers to
achieve the desired acoustical properties. The high density layer
22 conventionally is positioned outwardly of the vehicle structural
panel and may be desirably provided with a suitable decorative
coating or texture to conform with the decor of the vehicle
interior trim.
The formation of the acoustical panel in accordance with the method
aspects of the present invention conventionally employs a press
arrangement, such as shown in FIG. 3, comprising a lower platen 32,
which is stationarily supported on a base 34 and a movable upper
platen 36, guidably supported on guide rods 38 and reciprocable
therealong by a double-acting fluid-actuated cylinder 40. The lower
platen 32 can be provided with an inlet tube 42 for introducing a
suitable heating or cooling fluid thereto and similarly, the upper
platen can be provided with a conduit 44 for introducing a heating
or cooling medium thereto, depending upon the specific manner in
which a molding of the fibrous panel is effected.
Appropriately contoured mold or die sections, such as an upper mold
46, as shown in FIG. 4, and a lower mold 48, are adapted to be
secured to the opposed face surfaces of the upper platen and lower
platen, respectively. A composite fibrous pad 50, as shown in FIG.
4, is placed between the contoured upper and lower mold surfaces
and is molded to the appropriate contoured configuration of the
mold surfaces in accordance with one embodiment of the present
invention by the application of pneumatic pressure to the underside
of the pad, effecting a densification of the upper fibrous
layer.
In the specific arrangement shown in FIG. 4, the fibrous pad 50
comprises an upper or first layer 52, a lower or second layer 54
and a gas impervious flexible film or membrane 56 interposed
between the opposed face surfaces of the upper and lower fibrous
layers at a point intermediate the outer faces thereof. The
formation of composite fibrous pads of the foregoing type can be
achieved by a hand lay-up operation or, alternatively, by either
one of the techniques as schematically illustrated in FIGS. 7-9 of
the drawings.
As shown in FIG. 7, a composite fibrous pad or blanket 58 is
produced in accordance with one embodiment by preliminarily forming
an upper fibrous layer 60 which is stored in the form of roll stock
and providing a roll 62 of a flexible film 64. The upper fibrous
layer 60 and film 64 are advantageously applied in superimposed
relationship over a lower fibrous layer 66 as it is advanced toward
the right as viewed in FIG. 7 upon exiting from a suitable
garnetting or air-laying apparatus in which the lower fibrous layer
is formed.
The upper and lower fibrous layers are comprised of a mass of
randomly arranged fibers which may be comprised of any one or
mixtures of the types well known in the art, including those of
animal, vegetable and synthetic origin. Preferably, fibers are
selected which are of a length and strength and possessed of
inherent flexibility to enable the formation of a fibrous network
which is porous and possesses resiliency. Additionally, the
mechanical properties of the fiber are preferably such to enable
them to be passed through a garnetting or carding machine so as to
effect a combing and random orientation thereof into an elongated
fibrous blanket or batt without incurring any appreciable breakage
or disintegration of the fibrous filaments. Fibers which possess
mechanical properties of the foregoing type include
naturally-occurring vegetable origin fibers, such as cotton, hemp,
jute, ramie, sisal, cellulose, abaca, or the like. Typical
naturally-occurring animal origin fibers include wool, silk; hair
from cattle, horses and hogs; chicken feathers, etc,; while fibers
of a synthetic origin include cellulose acetate, viscose rayon,
nylon, vinyl chloride, protein base fibers such as casein and
soybean; glass fibers, ceramic fibers, or the like. In addition to
the foregoing mechanical properties, the selection of the fibers or
fibrous mixture is also made in consideration of their resistance
to thermal degradation at the elevated temperatures to which they
are to be subjected during the formation of the individual fibrous
layers, as well as during the molding operation.
Each of the fibrous layers are formed of a substantially uniform
desired thickness and density throughout by employing any one of a
variety of techniques well known in the art. For example, the
fibrous layers can be produced by passing the fibers or fibrous
mixture through a suitable garnetting or carding machine so as to
form a web which thereafter passes through a lapper in which an
overlapping of the web is performed until a batt or blanket of the
desired thickness is obtained. Alternatively, the fibrous blanket
can be produced by any one of the well known air-laying techniques
in which the individual fibers are deposited from an airborne
condition on a movable drum or foraminous belt to achieve the
desired thickness and density. Regardless of the specific manner in
which the fibrous layers are initially formed, the formation
procedure is carried out so as to introduce a suitable binding
agent in a finely particulated or powdered form into the matrix of
the fibrous mass, which upon subsequent setting in a manner as
subsequently to be described serves to integrally bond the fibrous
mass together and to further retain the molded fibrous layers in an
appropriately densified and contoured condition.
The initial thickness and density of each fibrous layer can be
varied consistent with the desired acoustical panel to be produced.
Ordinarily, fibrous blankets can be produced of a thickness as low
as about 1/4 inch up to about 21/2 inches or greater, while
thicknesses ranging from about 3/4 inch to about 11/2 inches are
usually preferred. The foregoing thicknesses when forming a fibrous
pad comprised of two such layers, provides an initial pad broadly
ranging from about 1/2 up to about 5 inches, and preferably, 11/2
to 3 inches in total thickness. The weight of the composite fibrous
pad comprising the plural fibrous layers and film interposed
therebetween may broadly range from as low as about 50 to as high
as 500 grams per square foot, while weights including the binding
agent incorporated therein of from about 100 grams to about 200
grams per square foot are usually preferred. While the thickness
and weight of the preliminarily formed upper fibrous layer 60 and
lower fibrous layer 66, as shown in FIG. 7, are usually
substantially the same, it will be appreciated that both the
thickness and initial weight thereof can be varied to provide a
final thermal and acoustical insulating or a trim acoustical panel
of the desired structure. The flexible film 64, accordingly, can be
interposed between the opposed face surfaces of the upper and lower
layer at any position intermediate of the outer face surfaces of
the layers and normally is spaced inwardly at least 1/8 inch from
the adjacent outer fibrous layered surface.
The plural density panel produced starting with a composite fibrous
pad of a thickness and weight as previously described or utilizing
individually molded layers in accordance with the alternative
method aspects hereinafter to be described is characterized as
comprising at least one densified layer integrally bonded to a
second less dense layer. The densified layer in accordance with the
present invention is of a density ranging from about 0.2 grams per
cubic centimeter (12.5 pounds per cubic foot) to a density as high
as about 1.3 gm/cc (81 lb/ft.sup.3), while densities of about 0.4
(25 lb/ft.sup.3) to about 1 gm/cc (62.5 lb/ft.sup.3) are
particularly preferred. The less dense layer, on the other hand,
may range from a density as low as about 0.04 gm/cc (2.5
lb/ft.sup.3) to as high as about 0.2 gm/cc (12.4 lb/ft.sup.3),
while densities of about 0.07 gm/cc (4.4 lb/ft.sup.3) to about 0.11
gm/cc (6.8 lb/ft.sup.3) are particularly satisfactory. The maximum
density of the densified layer is that established by the fibrous
material and binder agents employed, which are compacted to 100% of
theoretical density. More usually, the densified layer is densified
up to about 90% of theoretical density.
In order to achieve optimum thermal and acoustical insulating
characteristics, it has been found that the ratio of density of the
dense layer to the less dense layer may broadly range from about
2:1 up to about 32:1, while a density ratio of from about 4:1 to
about 15:1 is preferred in that it provides for ease of processing
of the panel and good acoustical and thermal insulating properties.
At density ratios in excess of about 32:1, difficulties are
encountered in the processing of the panel.
The foregoing density and density ratio limits are also applicable
to plural density panels comprised of three or more individual
layers. Usually, it is preferred that the dense layers are on the
outside of the panel, with the less dense layers disposed
therebetween. It is also preferred when more than two layers are
employed, that the layers alternate from high density to low
density to high density, etc., on passing from one face to the
opposite face of the panel.
The specific type and quanity of binding agents incorporated in
each of the fibrous layers can be varied consistent with the method
by which the plural density panel is molded. Conventionally,
powdered binding agents are introduced so as to effect a
substantially uniform impregnation of the fibrous matrix and are
employed in amounts ranging from as low as about 10% up to about
45% by weight based on the total weight of the fibrous layer. The
use of higher concentrations of binding agent provides for greater
rigidity of the resultant contoured panel. For most situations,
satisfactory results are obtained when the binding agent is
employed in an amout of from about 18% up to about 35% by weight of
the fibrous layer.
In accordance with one embodiment of the present invention, in
which pneumatic pressure is employed for effecting a molding and
densification of one of the fibrous layers, the binding agent
comprises a thermosetting resin of any of the types known in the
art, including phenol aldehyde resins, urea resins, melamine resins
or the like, of which the condensation product of phenol with
formaldehyde constitutes a preferred material. Additionally,
various lattices, either of natural or synthetic rubber, as well as
synthetic resin lattices, such as urethane or the like, can also be
satisfactorily employed for this purpose. When lattices are
employed, they are conventionally spray-applied in liquid form to
the fibrous web during the formation of the fibrous layer or
blanket.
In accordance with alternative embodiments of the method of making
the acoustical and trim acoustical panel, the binding agent may
comprise any one of a variety of thermoplastic heat softenable
resins which are characterized as being compatible with the fibrous
structure and have a heat softening range generally ranging from
about 200.degree. F. up to a temperature below that at which a
thermal degradation of the fibers occur. Preferably, such
thermoplastic resins are of a heat softening range within about
250.degree. F. to about 300.degree. F. Of the variety of
thermoplastic resins suitable for use in accordance with the
practice of the present invention, polyethylene, polystyrene,
polypropylene, acrylic, polyvinyl acetate, polyvinyl chloride
resins, polyvinyl chloride copolymers, or the like, can be
satisfactorily used, of which polyvinyl chloride itself constitutes
a preferred thermoplastic binder. A polyvinyl resin binding agent
in powder form which has been found particularly satisfactory is
commercially available from Union Carbide Corporation under the
designation VYHH, and comprises a copolymer of vinyl acetate and
vinyl chloride. As in the case of the thermosetting binding agent,
the thermosetting resin binder in powder form can be uniformly
distributed in the fibrous matrix upon emergence from the
garnetting machine during its passage toward the lapper or
alternatively, during the air-laying operation, whereby a uniform
dusting of the web or batt structure is effected.
It is also contemplated that the binding agent employed can
comprise a blend of a thermosetting as well as thermoplastic binder
of the aforementioned types to provide additional benefits in the
handling of the fibrous batts prior to and during the final molding
operation. According to one practice of the present invention, the
thermoplastic resin is employed in an amount ranging from about 15%
to about 95%, preferably about 50% up to about 75% by weight of the
total binder content, with the balance comprising a thermosetting
binding agent present in amount sufficient to integrally bond the
fibrous matrix together so as to retain its integrity during the
handling of the fibrous pad preliminary to the molding operation.
In the preliminary formation of the fibrous layers, it is usually
preferred to subject the outer face surfaces thereof to a
treatment, such as by the application of heat to effect a partial
curing of the thermosetting binding agent or a heat softening of
the thermoplastic binding agent in the surface stratum thereof so
as to impart additional integrity to the layers, facilitating
subsequent handling thereof and the formation of a composite
fibrous pad in a manner such as shown in FIG. 7.
The film 64 employed in forming the composite pad may be comprised
of any one of a variety of materials which are of sufficient
strength, heat resistance and flexibility to effect a pressure
molding of the fibrous pad into a trim panel in a manner as
subsequently to be described. For example, the film may be
comprised of a polyolefin resin, such as polyethylene or
polypropylene, acrylonitrile-butadiene-styrene (ABS), vinyl resins,
vinylidene resins and copolymers thereof, or the like. The film
itself need not be thermoplastic and should be of sufficient heat
stability to prevent disintegration during the pressure molding
operation until at least a partial setting of the binding agents is
effected to retain the contoured densified pad in the molded
condition. Thereafter, the film can disintegrate and become
diffused into the molded fibrous matrix.
Depending upon the specific material employed, the film itself may
range in thickness from about 1/2 mil (0.0005 inch) up to about 25
mils (0.025 inch), with thicknesses of from about 1 to 5 mils
generally being preferred. As the film is increased in thickness
beyond about 25 mils, it generally becomes less flexible and
thicknesses of the foregoing magnitude are more expensive and
ordinarily are not economically justified over the use of thinner
gauge films. Of the various materials suitable for use, polyolefin
polymeric films of a thermoplastic nature are conventionally
preferred.
In the embodiment illustrated in FIG. 7, the film 64 is interposed
between the upper and lower fibrous layers and is substantially
coextensive therewith. It is also contemplated that the film can be
interposed only at localized positions consistent with the intended
structural features of the multi-layered acoustical panel to be
produced. It is also contemplated that in addition to the
impervious film 64, additional films of a perforate character; that
is, pervious as a result of the application of perforations or
slits therethrough, can be employed at positions upstream from the
pressure side of the fibrous pad to impart further structural
features and acoustical properties to the resultant molded panel.
In any event, the surfaces of the film employed can be provided
with a suitable pretreatment to enhance the bondability of the film
to the opposed face surfaces of the fibrous layers. In this
connection, a suitable adhesive layer applied to the film surface
or to the fibrous layer can be used or, alternatively, the powdered
binding agent within the fibrous layers themselves can be adjusted
to provide the requisite adhesion.
Referring now to FIG. 8 of the drawings, an alternative technique
for forming a composite fibrous pad 68 is illustrated in which a
lower fibrous layer 70 is advanced toward the right, as viewed in
FIG. 8, as it emerges from a garnetting/lapper apparatus or an
air-laying apparatus and an impervious film 72, supplied in the
form of a roll 74, is applied over the upper surface thereof.
Thereafter, the lower layer 70 and film 72 passes beneath a lapper
device in which a series of laps 76, 78, 80 in the form of a
fibrous web from a lapper is applied to provide the requisite
thickness forming, in situ, an upper fibrous layer 82.
Still another alternative method for forming the fibrous pad is
illustrated in FIG. 9, in which a fibrous web 84 is integrally
formed and is advanced toward the right as viewed in FIG. 9 while
supported on a suitable conveyor or tenter frame. A slitter knife
or blade 86 is provided effecting a slitting of the fibrous web 84
into a lower fibrous layer 88 and an upper fibrous layer 90. The
upper fibrous layer 90 passes over an arcuate shoe 92 beneath which
a roll 94 containing a suitable impervious film 96 is positioned
and which is applied in overlying relationship against the opposed
slit surfaces of the lower and upper fibrous layers.
Regardless of the particular manner by which the composite fibrous
pad is produced, a molding thereof into a multiple-layered fibrous
acoustical panel is effected in accordance with the arrangement as
best shown in FIGS. 4-6. Referring specifically to FIG. 4, the
fibrous pad 50 is placed in overlying relationship on the mold
surface of the lower mold 48. The lower mold, as shown, is provided
with apertures 98 extending inwardly of the surface thereof and
disposed in communication with a plenum chamber 100 (FIG. 5)
connected to a pressurized source of gas, such as pressurized air,
through a port 102 connected to the plenum. The upper mold section
46 is provided with suitable heating elements 104, such as electric
heating elements or conduits through which a hot liquid such as oil
or the like is circulated, to effect a heating of the upper mold
section to a desired elevated temperature. The side edges of the
lower mold 48 are provided with a V-shaped plate 106, which is
adapted to coact with a trim or sealing bar 108 affixed to the
periphery of the upper mold 46, which upon a closing of the press
effects a sealing of the internal area of the composite fibrous
batt.
FIG. 5 illustrates fragmentarily the disposition of the composite
fibrous batt between the upper and lower molds upon a closure
thereof. The fibrous batt preferably is of a thickness greater than
the distance between the mold surfaces such that a partial
compaction thereof occurs upon closure of the molds. As will be
noted, the lower mold surface can also be provided with a
compression bar 110 for compacting both the upper and lower fibrous
layers 52, 56 against the upper mold surface for the purpose of
forming a densified strip or rib for reinforcing the panel. Upon a
closing of the mold to the position shown in FIG. 5, pressurized
gas, such as heated air, is introduced into the plenum 100 which
passes upwardly through the apertures 98 and through the lower
fibrous layer 54 against the film 56, causing a compaction and
densification of the upper fibrous layer 52 in shape-conforming
relationship against the upper mold surface. This is effected as
shown in FIG. 6 without any appreciable compaction of the lower
fibrous layer 54. In the specific embodiment illustrated in FIG. 6
in which the fibrous pad had been partially compacted during mold
closure, a partial expansion of the lower fibrous layer 54 occurs.
The effective pressure applied to the underside of the film 56 can
be varied over a broad range consistent with the desired
densification of the upper fibrous layer 52. While pressures in
excess of about 100 psig can be employed, effective pressures
within a range of about 20 up to about 50 psig are suitable for
most purposes. The specific pressure employed is also determined in
part on the initial density of the upper fibrous layer 52, as well
as the form and type, if any, of the texturing on the upper mold
surface to be imparted to the outer face of the densified layer.
Since the sealing of the peripheral portions of the composite pad
50 between the plate 106 and bar 108 ordinarily is not a perfect
seal, pressures slightly in excess of the effective pressure
desired are employed.
As shown in FIG. 6, the film 56 acts as a pressure membrane for
compacting the upper layer and for allowing expansion of the lower
fibrous layer 54 between the film and the lower mold surface. The
pressure applied is continued for a period of time to effect a
setting of the binding agent in both of the fibrous layers. In
accordance with a preferred embodiment, the binding agent employed
in both the upper and lower fibrous layers is a thermosetting
phenolic type resin, wherein the upper mold surface is heated to a
temperature generally ranging from about 350.degree. F. up to about
420.degree. F. to effect a curing thereof. Temperatures about about
450.degree. F. are generally undesirable in that a
thermodegradation of certain organic fibers may occur at
temperatures of this level, as well as spontaneous combustion of
heat sensitive fibrous materials. Ordinarily, dwell periods of from
about 10 seconds to about 3 minutes are satifactory for effecting a
substantially complete curing of the phenolic binding agent. The
curing of the binding agent in the lower fibrous layer 54 can be
facilitated by employing heated air introduced through the
apertures 98 for pressurizing the mold cavity. At the completion of
the molding operation, the pressure is first released whereafter
the press is opened and the multiple-density fibrous layered trim
panel of a shape-retaining contoured configuration is extracted.
Further trimming of the panel can be effected along the edges, as
well as for providing suitable apertures in the internal area
sections thereof.
In addition to the single-stage molding operation as described in
connection with FIGS. 4-6, multi-layered acoustical panels of the
present invention can also be produced in accordance with the
arrangement as illustrated in FIGS. 10 and 11. As shown in FIG. 10,
an upper precontoured fibrous layer 112 is applied in superimposed
relationship over a lower contoured fibrous layer of lower density
and adhesive is applied between the opposed faces thereof. The
resultant assembly is placed between upper and lower mated molds
116, 118 of the press shown in FIG. 11, and final molded in a
manner to effect simultaneous bonding of the two layers to each
other at their interface. The upper contoured layer 112 and lower
contoured layer 114 are comprised of the same fiber structure and
incorporating binding agents of the types heretofore described in
connection with the composite fibrous pad produced in accordance
with the procedure of FIGS. 7-9. The upper and lower pads are
individually molded employing a similar press arrangement to that
shown in FIG. 11 in which a substantially complete setting of the
binding agent is effected. A final contouring, sizing and curing or
setting of the binding agent is effected during the course of the
final molding operation as shown in FIG. 11.
As in the case of the single molding step previously described, the
upper fibrous layer 112 is preliminarily formed and molded to a
substantially high density approaching 100% theoretical density;
while the lowered contoured layer 114 is formed to a relatively
lower density, where upon assembly thereof a slight further
compaction can be effected to produce the desired final
densification and mating. A final setting of the binding agent,
such as a thermosetting curable type binding agent, can be effected
by providing the upper and lower mold sections 116, 118 with
suitable heating elements 120 of the type previously described in
connection with FIG. 4, for heating the fibrous layers to a
temperature generally from about 350.degree. F. to about
420.degree. F. Alternatively, heated air can be passed through the
fibrous layers to effect a curing thereof and to further accelerate
the setting of the adhesive layer between opposed face surfaces
thereof.
Another alternative satisfactory process embodiment for producing a
multiple-density layered fibrous acoustical panel is illustrated in
FIGS. 12 and 13. As shown, a lower preliminarily contoured fibrous
layer 122 is provided of a desired relatively low density produced
such as in the manner previously described in connection layers
112, 114 of FIG. 10. The upper, more dense fibrous layer 124 is
molded to a flat configuration and contains predominantly heat
softenable thermoplastic binding agents of the types heretofore
described, preferably in further combination with a minor quantity
of a thermosetting binding agent present in amounts sufficient to
integrally bond the fibrous matrix together and to retain its
integrity when the pad is subjected to elevated temperatures to
effect a heat softening thereof prior to molding. For this purpose,
the thermoplastic binder is preferably employed in amounts of about
50% up to about 80% of the total binder present.
The upper fibrous layer 124 is molded under pressure at an elevated
temperature to the desired density and in a manner to effect a
substantially complete curing of the thermosetting binding
constituent to form an integral pad. While still in a heat softened
condition, or alternatively, upon being reheated to a heat softened
condition generally in the range of from about 220.degree. F. to
about 400.degree. F., and preferably from about 250.degree. F. to
about 300.degree. F., the flat upper layer 124 is placed over the
preliminarily contoured lower density layer 122 while in the heat
softened condition, forming an assembly which is final molded in
the press arrangement illustrated in FIG. 13. The opposed faces of
the fibrous layers 124 and 122 are preferably provided with a
suitable adhesive coating to assure integral bonding therebetween.
In accordance with the press arrangement illustrated in FIG. 13,
the upper mold 126 is formed with cooling passages 128 through
which a suitable cooling fluid, such as a water-glycol mixture, is
circulated to cool the upper mold surface to a temperature below
that at which a rigidification of the thermoplastic binder in the
upper layer 124 is effected. The lower mold 130 is of an
appropriate contour and is matched to the contour of the upper
mold, whereby the composite acoustical panel is finish-molded to
accurate final thickness and density, while simultaneously
effecting a setting of the adhesive layer therebetween. After the
upper layer 124 has been cooled to a temperature at which the
thermoplastic binding agent has sufficiently hardened to retain the
shape of the upper mold surface, the molds are opened in accordance
with the press arrangement previously described, and the assembly
is extracted and subjected to further trimming action as may be
necessary or desirable, including the application of suitable
apertures, slits, etc., therein.
In accordance with an alternate embodiment of the single stage
pneumatic pressure molding process employing the mold arrangement
as illustrated in FIGS. 5 and 6, the upper mold section 46 is
provided with a plenum chamber 132 which is disposed in
communication with ports or apertures 134 which extend to the outer
face of the upper mold section. The arrangement of the plenum 132
and apertures 134 is similar to that of the plenum 100 and
apertures 98 in the lower mold section 48. The provision of such
apertures serve to vent entrapped air in the upper fibrous layer 52
providing for a more uniform densification thereof in response to
the pressure applied to the underside of the film 56. It is also
contemplated that the plenum 132 can be connected to a source of
reduced pressure or vacuum so as to provide for a vacuum assist in
combination with the pressure applied to the underside of the film
56 to effect a further densification of the upper fibrous layer.
Such a vacuum assist is particularly desirable when the upper mold
surface incorporates texturing to be imparted to the outer face of
the densified layer.
It is also contemplated that the single stage pneumatic pressure
molding step can be performed by the utilization of vacuum applied
to the plenum 132 relying on atmospheric pressure entering the
plenum 100 and apertures 98 of the lower mold section to effect
pressurization at the underside of the film and a compaction of the
upper fibrous layer. In such event differential pressures of up to
about 12 pounds per square inch can be applied to the film. In
either event, the vacuum applied to the upper fibrous layer can be
as great as about 3 psi absolute. Vacuums to provide absolute
pressures below about 3 psi are generally unattainable due to the
leakage of air along the edges of the mold through the densified
upper fibrous layer. Usually vacuums to provide an absolute
pressure ranging from about 7 up to about 11 psi are suitable for
most molding operations.
While it will be apparent that the invention herein described is
well calculated to achieve the benefits and advantages set forth
above, it will be appreciated the invention is susceptible to
modification, variation and change without departing from the
spirit thereof.
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